Saturday, July 16, 2011

A bony toothed bird from the Purisima Formation, part 2

After I got the bone identified as a bird, I emailed pictures to my colleague N. Adam Smith, who at the time was a Ph.D. student at University of Texas at Austin, studying with Julia Clarke. We both agreed on the identification of the specimen as a pelagornithid, and also agreed that it could be written up quickly, and we immediately began working on the manuscript. This was the fastest paper I ever wrote - partially because each of us did about 50% of the work, and we went through a bazillion drafts (a new draft every 24-36 hours for four weeks in September and October), and we finally submitted it on Halloween.

We were pretty anal about properly figuring and labeling all the anatomic structures of this specimen in our paper; we were wholly dissatisfied with previous papers which had not labeled the relatively divergent anatomical structures of pelagornithid humeri sufficiently. Many anatomical features are fairly modified relative to non-pelagornithids, and without adequately labeled (or unlabeled) figures, it is difficult for the non-specialist to interpret their morphology; we thought we'd do everyone a favor and do it properly. One exception is Bourdon et al. (2010), who studied Eocene pelagornithids from Morocco (whose paper was also not out yet when we submitted our article).

Figure 2 from our paper, highlighting the anatomical structures of UCMP 219007.

A comparison of humeri of pelagornithids and modern pelecaniform and procellariiform birds. A- Pelagornis sp. (UCMP 219007); B- Pelagornis chilensis, late Miocene, Bahia Inglesa, Chile (holotype, from Mayr and Rubilar-Rogers 2010); C- Pelagornis miocaena, Miocene, France; D- Pelagornis sp., Pisco Formation, Peru (Pliocene); E- Morus bassanus, Gannet, extant (CAS specimen); F- Phoebastria irrorata, Waved Albatross, extant (CAS specimen); G - cf. Macrodontopteryx (synonymized with Dasornis iby Bourdon, 2010), Eocene, Belgium; H- Pelagornis mauretanicus, Pliocene, Morocco.

Many features of pelagornithids (and specifically, Pelagornis spp.) are highly divergent relative to other pelecaniformes (as you can see above, compared with Morus). Additionally, as you can see, our specimen is one of the most well preserved pelagornithid humeri now known, even more so than the beautiful holotype of Pelagornis chilensis, the humerus of which still has quite a bit of matrix encrusted and glued onto the bone, obscuring some of the fossae. One of the pneumatic fossae is actually pneumatized, and bears a pneumatic foramen that appears to connect to the internal cavity of the bone, a condition we had not read about or observed in any fossil or modern relative.

Shaded drawing I made and used for figure 3 of our paper, showing the pneumatic foramen.

Lastly, for our paper I thought I would try a skeletal reconstruction of Pelagornis. It was on my to-do list for the paper, and we already had a couple of drafts sent back and forth when Pelagornis chilensis graced the cover of JVP: it couldn't have been more timely. Although not in the original paper, associated with the press release were several skeletal reconstructions. I emailed the artist Carlos Anzures in Chile to ask for permission to modify it for our study. Well, I didn't just modify it; I redrew it by hand, reposed it, inked the drawing on vellum, and then edited the image in adobe illustrator, to eventually get something like what you see below:

Part of Figure 1 of our paper, showing the skeletal reconstruction of Pelagornis.

Next time: more on pelagornithid evolution and ecology, as well as biogeography and the implications of our find.

Bourdon, E., Amaghzaz, M., and Bouya, Baadi. 2010. Pseudotoothed birds (Aves, Odontopterygiformes) from the Early Tertiary of Morocco. American Museum Novitates 3704:1-71.

Mayr, G., and D. Rubilar-Rogers. 2010. Osteology of a new giant bonytoothed bird from the Miocene of Chile, with a revision of the taxonomy of Neogene Pelagornithidae. Journal of Vertebrate Paleontology 30:1313–1330.

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